Electrical timing circuit



29, 1964 J. L. LUCKADOO ELECTRICAL TIMING CIRCUIT Filed May '21, 1962 m M w W. W Sum en -39 M 9W NN M p M W NM .w L new r 23 I. mm d fi xxdfi E M no.1 fioesw 5% Q 2-3 kmkoo xww 2 5 mm. QRW er. )1? v 3v N uxn x \VN Wm T Patented Dec. 29, 1964 3,163,303 ELECTRICAL TIMING CIRCUIT James Laurence Lucliadoo, Eucheystown, Md., assignor to Metronics, Cor-12., Frederick, Md., a corporation of lt l'aryland Filed May 21, 1962, Ser. No. 196,103 7 Claims. (Cl. 317-142) The invention relates to an electrical timing device, and particularly to a timing device which, when a switch is closed, operates a relay immediately and maintains this relay energized for predetermined period of time.

Many electrical devices, particularly measuring instruments and similar devices, and especially those used in airplanes, are often subjected to variations in the voltage imposed upon them for short periods of time. In testing such devices, it is necessary to subject them to conditions similar to the conditions they may face in actual use, in order to make sure that they can operate satisfactorily after the occurrence of such irregular conditions.

, The primary purpose or" the invention is to provide a timing circuit which will make it possible to subject an instrument or the like to such abnormal voltage conditions, for periods of time at least equal to the time that such conditions would be likely to exist in practice, so as to determine whether or not the instrument canbe reliable and will operate after such conditions have occurred.

Another object of the invention is to provide a circuit in which, when a manual switch is operated to energize the relay, operation of the relay closes an additional switch in such a Way as to prevent deenergization of the relay if the manual switch is released before the time for which the circuit is set has expired, and also to prevent interference with the action of the circuit by a reclcsing of the manual switch until the time for which the circuit has been set has expired.

Another object of the invention is to provide a circuit which, Within reasonable limits, maintains a predetermined time constant regardless of variations in the voltage applied by the sourceof potential.

Further objects an advantages of the invention will appear from the following description, particularly when taken in conjunction with the accompanying drawing, which form a part thereof.

The drawing shows a circuit embodying the invention.

As shown, this circuit is intended to be used for energizing a relay 2 for a predetermined adjustable period of time. This relay may operate a switch 4, which either imposes an increased cur-rent on an instrument to which it is connected for a predetermined period of time, or in some way reduces the current applied, depending upon the variation of the conditions to which the instrument is likely to be subjected in practice.

The device includes a power supply 6, which may be for instance 24 v., which is connected to one terminal of the relay 2. The other terminal of the relay is connected to the collector of a PNP transistor 8, which has its emitter connected to ground through a silicon diode it), which may be a 1N1692. The base of the transistor 8 is connected through a resistance 14- to the collector of a transistor 12. This collector is also connected to ground through resistance 16. The emitter of the transistor 12, which is an NPN transistor, is connected to the slider of a voltage divider 18, which is connected through resistance 20 to the power supply 6. Transistor 12 may be a2N1306.

Voltage divider 13 is also connected by resistance 22 to ground.

Resistances 24, 26 and 28 connected in series to the power supply are connected to one plate of a condenser 30. The line between resistance 28 and condenser 30 is connected to ground through a diode 32, which is conducting until the charge on the plate of condenser 30 exceeds a predetermined value, at which time the diode 32 becomes non-conducting. In other words, it is inversely voltage dependent. I

A switch 34 is provided which can connect in parallel with resistances 24, 26 and 28, either two resistances 36, 38 or two other resistances 40, 42. This switch has four positions.

In each of the other three positions, the power supply input is connected in circuit, whereas in the first position, switch 34 is dead, and resistances 24, 26 and 28 only are connected between the plate of condenser 30 and the power supply. In the other two positions, either resistances 36 and 38 or resistances 40 and 42 are connected in parallel with the resistances 24, 26 and 28.

The other terminal of condenser 30 is connected to a switch 44, having two positions. In the right-hand normal position, in which it is shown, this switch connects the plate through resistance 46 to the power supply, while in the other positions it connects it through line 48 to ground.

Connected with and operated by the relay 2 is a switch 56, which when closed connects the left-hand terminal of the condenser 30 to ground.

This arrangement operates as follows:

Assuming the parts to be in the position shown, the left hand terminal of capacitor 30 bears a negative charge, since it is connected with the power supply 6.

The right-hand terminal has a positive charge with respect'to the opposite terminalbecause of the connection to ground through diode 32.

Assuming the parts to be as shown, with the switch 34 in the second position, so that none of the resistances 36,

38,40 or 42 are connected in the circuit, the switch 42 is operated manually and grounds the left-hand plate of condenser 30. A discharge path for the capacitor is now provided and the left hand plate of the capacitor goes from 24 v. to ground potential. This causes the potential on the righthand plate to become positive with respect to ground, as +24 v., and the increased difference between this potential and the negative potential of the power supply is suificient to render transistor 12 conducting. Likewise, the potential on the right-hand plate is high enough to render diode 32 non-conducting and therefore remains on the plate.

I The voltage divider is setso that it can establish a voltage of anywhere between 1.97 v. and -ll.8 v. When a large positive charge is established on the righthand plate of condenser 30, it will produce at point 52, between resistances 24 and 26, which is connected to the emitter of the transistor 12, a charge which is positive, or at leastlcss negative than the charge on the base of the transistor resulting from the setting of voltage divider 18. This will render the transistor 12 conducting, and will then impose a negative voltage through resistance 14 on the emitter of transistor 8, rendering it conducting and thus connecting the other terminal of the relay 2 to ground, energizing the relay. This relay is shunted by a diode 54. p

-Now as the right-hand'plate of the condenser 30 discharges back to the power supply 6, the potential at point 52 will gradually become less, until it becomes lower (or more negative) than the potential produced by voltage divider 18. When this happens, transistor 12 will become non-conducting, as will transistor 8, and'the relay will bode-energized. It is clear that by setting the voltage divider '18 to various values, the time required for the potential at point 52 to become more negative than that set on the voltage divider will vary. The setting of the voltage divider thus determines the timing of the circuit.

Qbviously'also by cutting in resistors 36, $8 or 40, 42 in parallel with resistances 2 4 26, 28, the time of discharge of the condenser 30 can be reduced, so that these two positive resistances serve for adjustment to different time ranges, while the voltage divider 18 serves for Vernier adjustment within each time range.

The energization of the relay 2 closes switch 50, which grounds the left-hand plate of condenser 30. Even if the manual switch is released and returns to its normal position, it cannot disturb the charge on the righthand side of the condenser 30, since the left-hand plate remains grounded as long as the relay isenergized.

Likewise, because the voltage at point 52 and the potential on the voltage divider 18 are both derived from and dependent upon the same power supply 6, variations in the power supply within a moderate range, such as 20%, are substantially equalized. That is, the time interval is determined by the interaction of two variables which are both a function of and proportional to the direct current supply voltage.

As soon as the relay is de-energized, switch 50 is opened. The circuit is then ready for another operation.

While 1 have described herein one embodiment of my invention, I wish it to be understood that I do not intend to limit myself thereby except within the scope of the claims hereto or hereinafter appended.

I claim:

1. A control circuit for operating a relay for a predetermined length of time comprising a source of electric potential having one terminal connected to ground, a capacitor, first means for selectively connecting one terminal of said capacitor to the other terminal of said source and to ground, a relay, second means connecting one terminal of said relay to such other terminal of said source, third means connected to the other terminal of said capacitor for connecting the other terminal of the relay to ground when said first capacitor terminal is tricpotential having one terminal connected to ground,

a capacitor, first means for selectively connecting one terminal of said capacitor to the other terminal of said source and to ground, a relay, second means connecting one terminal of said relay'to such other terminal of said source, resistance means connecting the other terminal of the capacitance to said one terminal of the relay,,third means connected to such other terminal of an intermediate point of said resistance means and responsive to the potential at such point for connecting the other terminal of said relay to ground when said first capacitor terminal is connected to ground'by said selective connecting means, fourth means normally grounding such other terminal of the capacitor, said fourth means being nonconductive when the/potential at such other capacitor terminal exceeds a predetermined value, andswitch means connected to the first capacitor terminal and operated by encrgization of said relay to connect said first capacitor terminal to ground.

3. In a device as claimed in claim 2, fifth means for selectively connecting further resistances in parallel with such resistance means.

4. A control circuit for operating a relay for a predetermined length of time comprising a source of electric potential having one terminal comiected to ground, a capacitor, first means for selectively connecting one terminal of said capacitor to the other terminal of said source and to ground, a relay, second means connecting one terminal of said relay to such other terminal of said source, resistance means connecting the other terminal of the capacitor to said one terminal of the relay, a voltage divider connected to said other terminal of said source, third means connected to an intermediate point of said resistance means and to said voltage divider and responsive to differences of the potential thereon for connecting the other terminal of said relcy to ground whensaid first capacitor terminal is connected to ground by said selective connecting means, fourth means normally grounding such other terminal of the capacitor, said fourth means being non-conductive when the potential at such other capacitor terminal exceeds a predetermined value, and switch means connected to the first capacitor terminal and operated by energization of said relay to connect said first capacitor terminal to ground.

5. A control circuit for operating a relay for a predetermined length of time comprising a source of electric potential having one terminal connected to ground, a capacitor, first means for selectively connecting one terminal of said capacitor to the other terminal of said source and to ground, a relay, second means connecting one terminal of said relay to such other terminal of said source, resistance means connecting the other terminal of the capacitance to said one terminal of the relay, a voltage divider connected to such other terminal of said source, third means connected to an intermediate point of said resistance means and to said voltage divider and responsive to differences of the potential thereon for connecting the other terminal of said relay to ground, and fourth means normally grounding such other terminal of the capacitor, said fourth means being non-conductive when the potential at such other capacitor terminal exceeds a predetermined value.

,6. In a timing circuit, a relay which is to be operated for aselected period of time, a source of electric potential having one terminal connected to ground, a capacitor, resistance means connecting one terminal of said capacitor to the other terminal of said source, first means for selectively connecting the other terminal of said capacitor to such other terminal of said source and to ground, second means connecting one terminal of said relay to such other terminal of said source, third means connected to a point of said resistance means and responsive tov changes in the potential at such point to connect the other terminal of the relay to ground, and fourth means normally grounding such other terminal of the capacitor, said fourth means being non-conductive when the potential at such other capacitor terminal exceeds a predetermined value.

7. In a circuit as claimed in claim 6, means controlled by said relay for connecting said other terminal of the capacitor to ground as long as the relay is energized.

References Cited by theExaminer UNITED STATES PATENTS 2,950,422 8/60 Purkhiser 3 l7142 3,005,935 10/61 Wood -3l7l48.5 3,071,712 1/63 Porter 3l7142 SAMUEL BERNSTEIN, Primary Examiner. 

1. A CONTROL CIRCUIT FOR OPERATING A RELAY FOR A PREDETERMINED LENGTH OF TIME COMPRISING A SOURCE OF ELECTRIC POTENTIAL HAVING ONE TERMINAL CONNECTED TO GROUND, A CAPACITOR, FIRST MEANS FOR SELECTIVELY CONNECTING ONE TERMINAL OF SAID CAPACITOR TO THE OTHER TERMINAL OF SAID SOURCE AND TO GROUND, A RELAY SECOND MEANS CONNECTING ONE TERMINAL OF SAID RELAY TO SUCH OTHER TERMINAL OF SAID SOURCE, THIRD MEANS CONNECTED TO THE OTHER TERMINAL OF SAID CAPACITOR FOR CONNECTING THE OTHER TERMINAL OF THE RELAY TO GROUND WHEN SAID FIRST CAPACITOR TERMINAL IS CONNECTED TO GROUND, RESISTANCE MEANS CONNECTING SUCH OTHER CAPACITOR TERMINAL TO SUCH OTHER TERMINAL OF SAID SOURCE, FOURTH MEANS NORMALLY GROUNDING SUCH OTHER TERMINAL OF THE CAPACITOR, SAID FOURTH MEANS BEING NONCONDUCTIVE WHEN THE POTENTIAL AT SUCH OTHER CAPACITOR TERMINAL EXCEEDS A PREDETERMINED VALUE, AND SWITCH MEANS CONNECTED TO THE FIRST CAPACITOR TERMINAL AND OPERATED BY ENERGIZATION OF SAID RELAY TO CONNECT SAID FIRST CAPACITOR TERMINAL TO GROUND. 